On the most exposed types of rocky shore, mussels are ousted by a special type of alga called a sea palm, which only grows on the north-west coast of North America. The sea palm has a crown of leaves at the top of its rubbery stem which it uses to harness the power of the waves and attack the mussels. In spring a sea palm may attach itself to an individual mussel. When the sea palm is mature and out of water, it will produce spores which trickle down its leaves into the mussel bed. Later, when autumn storms come, the waves may catch the plant's fronds and rip it, and the mussel it holds, off the rock. The spores left by it and its neighbouring plants can thus grow on that bare rock, thanks to the sacrifice of that first plant.